Curie point control device



March 4, 1958 E. o. OLSEN 2,82

CURIE POINT CONTROL DEVICE Filed Aug. 4, 1955 4 Sheets-Sheet l 4 I /I3 I5 I2 =4 I0 I o v I FIG. I I 7 FIG. 11

. PARALLEL AM RESONANCE 20 I9 I (CII 22 FIG. IIIII PARALLEL SERIES RESONANCE RESONANCE (mm) I I I "J LL] 0 o I 5 5 I Q o E I E I Z l E I I I I INDUCTANCE 0F L c,=c0NsTANT) INDUCTANCE OF L2IC2=CONSTANTI INVENTOR. FIG. III 7 4 g EVERETT o. OLSEN AGENT .M 1 E. o. OLSEN 2,825,868

CURIE POINT CONTROL DEVICE Filed Aug. 4, 1955 4 Sheets-Sheet 2 SERIES RESONANCE (C2) 27 0 26 29 I i I k 28 l FIGEII IN VEN TOR.

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AGENT March 4, 1958 E. o. OLSEN 2,825,868

CURIE POINT CONTROL DEVICE Filed Aug. 4, 1955 4 SheefsSheet s 'l/IIIIIIIIIIIIIIIIIIllIllIIlIIll/Il IIIIIIIIIIIIIIIIIIIII'IIIIIIIIIIIIIIIIIIIIIIII'IIIIIIII'IIIIIIIIII INVENTOR. EVERETT O. OLSEN March 4, 1958 E. o. OLSEN CURIE POINT CONTROL, DEVICE Filed Aug. 4, T 1965 4 Sheets-Sheet 4 INVENTOR.

EVERETT O. OLSEN llllrllllll P 4 AGENT United States Patent Ofiiice CURIE POINT CONTROL DEVICE Everett 0. Olsen, Wrentham, boro Company, Foxhoro, sachusetts Mass., assignor to The Fox- Mass., a corporation of Mas- This invention relates to electrical circuit devices as aifected by temperature, and has particular reference to such devices wherein the Curie point of an element of the device is a factor in the operation thereof.

All substances having ferro-magnetic properties have a definite temperature of transition at which the phenomena of ferro-magnetism disappear and the substances become merely para-magnetic. This temperature is called the Curie point and is usually lower than the melting point. As an example of this condition in an embodiment of this invention: when the core of a transformer is heated to its Curie point, the degree of coupling between the primary and secondary windings of the transformer is greatly reduced.

Accordingly, specific changes may be brought about in devices wherein the ferro-magnetic properties of a substance have eifect, by bringing the substance to its Curie pigint and thus substantially reducing the ferro-magnetic e ect.

This invention provides a novel device for making use of the Curie point. Specifically, this invention is concerned with electrical coils and ferro-magnetic property material cores therefor, and the operation of a device embodying this invention comprises bringing the core to its Curie point and thereby substantially changing the electrical effect of the coil-core combination.

In this invention this action is provided by a heating element mounted in heating relation with respect to the core, for example, a resistor mounted adjacent to the core.

This invention is exemplified by an electrical circuit combination of a coil and core assembly with a resistor mounted as a heating element with respect to the core and with the circuit so arranged electrically as to control the current in the resistor as a function of the temperature of the core in relation to the Curie point of the core, in such a manner that reduced magnetic effect in the coilcore arrangement results in reduced current in the resistor.

It is therefore an object of this invention to provide a new and improved Curie point control device.

Other objects and advantages of this invention will be in part apparent and in part pointed out hereinafter, and in the accompanying drawings, wherein:

Figure I is a circuit diagram of a parallel impedance device embodying this invention;

Figure II is an illustration of a combination of the circuit of Figure I with an oven to provide a Curie point controlled oven;

Figure III illustrates a parallel arrangement of a resonance type circuit embodying this invention;

Figure IV is a parallel resonance curve illustrating the impedance variance which may occur in the circuit of Figure III;

Figure V is a series resonance curve illustrating the impedance variance which may occur in the circuit of Figure VI;

Figure VI illustrates a series arrangement of a resonance type circuit embodying this invention;

2,825,868 Patented Mar. 4, 1958 Figure VII is an illustration of a combination of the circuit of Figure V1 with an oven to provide a Curie point controlled oven;

Figures VIII, IX and X show circuit diagrams of a transformer device embodying this invention, with diiTerent current limiting elements, and with Figure X; especially, illustrating a combination of a transformer type circuit with an oven to provide a Curie point controlled oven; and

Figure XI shows a combination of Curie point furnace control devices according to this invention.

For purposes of explanation, the circuits according to this invention may be catalogued in three classes: (A) Parallel impedance circuits, Figures I and Ii; (B) resonance circuits, Figures III-VIII inclusive; and (C) transformer circuits, Figures VIII-IX inclusive.

There are also three combination illustrations set forth herein: (a) furnace control, Figure VII; (b) thermocouple cold junction compensation, also Figure VII; and (c) constant D. C. source, Figure XI.

However, as many embodiments may be made of this invention, and as changes may be made in the embodiments set forth above without departing from the scope of the invention, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative only and not in a limiting sense.

This invention is concerned with the Curie point of the core of an electrical coil and core combination. Such a core is formed of material having ferro-magnetic properties, but does not necessarily have iron as an ingredient.

Different materials have different Curie points, and a factor of consequence in a core for this invention is its permeability. While this invention is not limited to materials of particular Curie points, it is ordinarily preferable because of insulation problems, to choose a material with a relatively low Curie point, of the order of 400 C. or lower. In most instances it is preferable also to select a material of relatively high permeability in relation to the selected Curie point, in order to provide an effective device. It is also desirable to use a material which is characterized by sharp change in permeability at its Curie point.

Examples of such material are:

Nickel: 662 F.

Cobalt: 2012 F.

Nickel, 2% chrome: 464 F. to 536 F.

M0nel-Ni 67.74%, Cu 29.62%, iron 2.92%: 152 F.

Midvale E. I. 562-Ni 31.35%, chromium 11.80%, Fe:

JessopNi 32.40%, Fe 66.91%, carbon 14%, small manganese: 291 F.

Invar36% Ni-Fe: 485 F.

In general, the operation of a device according to this invention is as follows: A coil and core combination is provided with a particular impedance value as established by the selected materials and their dimensions and arrangement. This impedance is established with the core at a temperature below its Curie point. However, when the core temperature is raised to its Curie point, the core loses a substantial part of its ferro-magnetic properties. Thus the core is essentially no longer effective in contributing to the impedance of the coil-core combination. Accordingly, we have an impedance reducing action.

According to the conditions involved in a particular circuit of this invention a current limiting impedance is either designed into the main elements of the device, or added as an extra element, so that a current change in the circuit due to the above-mentioned reduced impedance is not harmful.

Figures I and II illustrate a parallel impedance circuit.

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In Figure I the circuit is provided with a coil 10, a core 11 therefor, and a resistor 12 in parallel with the coil 10. The resistor 12 is mounted as a heating element in relation to the core 11, as indicated by a dotted line 13. This heating relation may be accomplished'in a simple form by mounting the resistor on, or closely adjacent to, the core 11. A current limiting element 14 is provided, in series with the parallel arrangement of the coil and the resistor 12. While the current limiting element 14 may readily be a resistor, as shown as a dotted line therein, a condenser or a coil may be substituted therefor.

In the operation of the Figure I circuit, when A. C. is applied thereto, the core 11 is initially at a temperature below its Curie point. Thus the core 11 is effective in increasing the impedance of the coil 10 by increasing its inductance. Under these conditions this arrangement acts as a voltage divider, with the greater part of the current routed through the resistor 12, and the heat from the resistor is applied to the core 11. When the temperature of the core reaches its Curie point the core, to a large degree, loses its ferro-magnetism and therefor no longer is effective in increasing to any substantial degree the impedance of the coil 10. Accordingly, this impedance is reduced and the division of current between the coil 1!) and the resistor 12 is changed, with more current passing through the coil 10 and less current passing through the resistor 12. With the resistor current thus reduced the heating effect thereof is reduced, and the temperature of the core 11 falls below the Curie point of the core. In this fashion the core 11 regains its ferro-magnetism, the impedance of the coil 10 is increased, the voltage across the resistor 12 is increased, and hence the current through the resistor 12 is increased and the resistor 12 again becomes an active heating element to again raise the temperature of the core 11 to its Curie point. Through this form of action the circuit is stabilized and the temperature of the core 11 is automatically controlled in relation to the Curie point of the core.

Figure II illustrates the combination of the circuit of Figure I with an oven 15 to provide a Curie point temperature controlled oven.

Figures III-VII inclusive all relate to the resonance type of Curie point circuit embodying this invention. Figure VII illustrates the combination of the circuit of Figure VI with an oven 16 to provide another form of a Curie point temperature controlled oven. The circuit of Figure III could readily be substituted for the Figure VI circuit in the combination illustration of Figure VII.

Of the impedance curve graphic Figures IV and V, Figure IV relates to the parallel circuit of Figure III, and Figure V relates to the series circuit of Figure VI.

Figure III comprises a load resistor 17 as a heating element in parallel with a parallel combination 18 of a resonance arranged condenser 19 and coil-core unit 20- 21. The resistor 17 is mounted in heating relation with the core 21 as indicated by the dotted line 22. This circuit is also provided with a current limiting device 23, like that (14) in Figure I, in series with the parallel arrangement of the condenser 19, the coil 20 and the resistor 17. The condenser 19 and the coil-core (20-21) are arranged for resonance with the supply frequency whenever the temperature of the core 21 is below its Curie point. As may be noted in Figure IV this condenser-coil parallel combination has high impedance at resonance, with respect to an applied power frequency which is essentially constant, and the impedance drops oft" sharply with a comparatively small change in the impedance relation between the condenser. (19) and the coil'core combination 2tl-21. Accordingly, when the temperature of the core 21 is below its Curie point the condenser-coil combination 18 has high impedance, and there is substantial current flow through the resistor 17. On the other hand, when the resistor 17 has heated the core 21 to the Curie point of the core, the impedance of the coil-core combination 2021 drops sharply, and

this results in a detuning action with a sharp drop (Figure IV) in the impedance of the parallel combination 18. As a result, there is a substantial reduction in the current through the resistor 17, so that its heating effect is reduced and the temperature of the core 21 drops below its Curie point. Thereafter the cycle continues, with the core 21 again being heated, and the core 21 being controlled to its Curie point in essentially the same manner as discussed hereinbefore with respect to the circuit of Figure I.

The Figure VI and VII series resonance circuit comprises a series resonance arrangement 24 of a condenser 25 and a coil 26, a core 27 associated with the coil 26, and a load resistor 28 in series with the series resonance arrangement 24. The load resistor 28 is mounted as a heating element with respect to the core 27, as indicated by the Figure VI dotted line 29, and the Figure VII close association of the core 27 and the resistor 28.

The condenser 25 and the coil-core combination 26- 27 are arranged for resonance with the supply frequency whenever the temperature of the core 29 is below its Curie point. As may be noted in Figure V, this condenser coil series combination has a low impedance at resonance, and the impedance rises sharply with a comparatively small change in the impedance relation between the condenser 25 and the coil-core combination 26-27. Accordingly, when the temperature of the core 27 is below its Curie point the condenser-coil combination 24 has low impedance, and there is substantial current flow through the resistor 27. On the other hand, when the resistor 28 has heated the core 27 to the Curie point of the core, the magnetic effect of the coil-core combination 2627 drops sharply with the result that the condenser-coil combination 24 is tuned ofi resonance and the impedance of the condenser-coil combination 24 rises sharply (Figure V). As a result the current in the resistor 28 is reduced substantially and the temperature of the core 27 drops below its Curie point. Thereafter the cycle continues, with the core 27 again being heated to its Curie point until a balance is achieved which holds the temperature of the core 27 essentially at the Curie point of the core 27.

The Figure VII arrangement, therefore, provides an oven which is automatically held to a particular temperature as determined by the Curie point of the core 27. Accordingly, a thermocouple system cold junction compensation device is readily provided by mounting a thermocouple 30 within the oven of Figure VII, preferably by attaching the thermocouple to the core 27. Thermocouple leads 31 are provided for electrical connection to a conventional thermocouple system (not shown) so that the thermocouple 30 provides a constant cold junction reference value.

It may be noted, in the circuit of Figures VI and VII, that the condenser 25 is a current limiting device so that elements such as item 14, Figure I and 23, Figure III, are unnecessary in the series resonance arrangement. I

Figures VIIIXI inclusive all relate to the transformer type of Curie point circuit embodying this invention. Figure X illustrates the combination of this type of circuit with an oven 32 to provide a Curie point temperature controlled oven. Either of the circuits of Figures VIII and IX could readily be substituted for the Figure X circuit in the combination illustration of Figure X. The circuits of Figures VIII-IX are identical except for the current limiting devices therein, indicated as 33, 34, 35, and 36 respectively. The current limiter in Figure VIII is a resistor 33, in Figure IX a condenser 34, in Figure X a coil 35, and in Figure XI block 36 indicates that any of these current limiters may be used in the structure of Figure XL The current limiters indicated herein are so indicated by way of illustration. Any suitable current limiting device or arrangement may be used in their place, as desired.

Figure VIII comprises a transformer circuit wherein transformer 37 has a primary winding 38, a secondary Winding 39, and a core 40. The current limiter resistance 33 is arranged in series with the primary winding 38, and a load resistor 41 is connected across the secondary Winding 39 as a heating element for the core 40, as indicated by the dotted line 42.

In the transformer type of circuit, Figures VlII-Xl', the degree of coupling between the primary and secondary of the transformer is the factor which is varied in relation to the Curie point of the transformer core 40.

When the transformer core 40 is at a temperature below its Curie point, it has substantial ferro-magnetic properties so that the coupling between the transformer windings 38 and 39 is substantial. Thus the current value in the load resistor is relatively high. When the core 40 has been heated to its Curie point by heat from the resistor 41, the core becomes para-magnetic and the coupling between the transformer windings is substantially reduced. Thus the current in the load resistor 41 is also reduced, and the temperature of the core 40 drops below the Curie point of the core and regains its ferro-magnetic properties. Thereafter, the resistor 41 again heats the core to its Curie point and the cycle is repeated until a balance is achieved which holds the temperature of the core essentially at the Curie point of the core.

Figure XI illustrates a combination of two transformer type circuits each being a part of a combination with an oven, to provide a pair of Curie point controlled oven arrangements. The transformer core 40 in oven #1 is selected or formed so as to have one Curie point and the transformer core 40 in oven #2 is selected or formed so as to have a second and different Curie point. Thus the two ovens are automatically controlled to difierent temperatures as related to the difierent Curie points of their respective transformer cores. A thermocouple 43 is located in oven #1 and a thermocouple 44 is located in oven #2. These thermocouples may be placed in the general ambiency within the ovens, as shown, or they may each be secured directly to their respective transformer cores.

The thermocouples are electrically connected through leads in a difierential arrangement, and a constant D. C. source is thus provided from the constant temperature dififerential between the ovens or their transformer cores, according to the arrangement of the thermocouples in relation to their respective cores. It is Within the intended scope of this invention that either parallel impedance circuits or resonance circuits, or both, according to this invention may be used in place of the Figure XI transformer circuits.

This invention, therefore, provides a new and improved Curie point control device wherein a heating element is provided in heating relation with the core of a coil-core combination, and wherein the heating effect of the heating element with respect to the core is a function of the magnetic efiect of this coil-core combination.

I claim:

An alternating current circuit of the character described, comprising a parallel arrangement of a condenser and an inductance coil unit which are related for resonance, a magnetic material core as a part of said coil unit, a heating resistor in parallel with said condenser-coil arrangement, said resistor being arranged to heat said core, and current limiting means in protective relation with the elements of said circuit.

References Cited in the file of this patent UNITED STATES PATENTS 1,655,847 Seibs Jan. 10, 1928 1,697,148 Spooner Jan. 1, 1929 2,513,779 Bailey July 4, 1950 2,644,738 Gardner July 7, 1953 

